1. Technical Field
Embodiments described herein relate to a wiring board and a method for manufacturing the wiring board.
2. Related Art
Increase in density of a mounted semiconductor chip has heretofore advanced, so that reduction in thickness of a wiring board and increase in density of wiring patterns have been required. To meet such requirements, a wiring board after removal of a core board (support board) having high rigidity and thicker than an interlayer insulating film, that is, a so-called coreless board has been proposed.
In a basic process of the coreless board, a temporary board is first prepared as a support board. A wiring layer serving as pads is formed on the temporary board. Then, after a required number of wiring layers and insulating layers are built up, the temporary board is finally removed.
A technique of providing any one of formed insulating layers in this type coreless board as an insulating layer improved in mechanical strength by a reinforcing material to reduce warping of the board has been proposed recently (e.g. see JP-A-2007-96260).
However, in the wiring board having the reinforcing material-containing insulating layer, there is a problem that fine wirings cannot be formed on the reinforcing material-containing insulating layer. To describe in detail, for example, when wiring patterns are formed on the reinforcing material-containing insulating layer by a semi-additive method, the upper surface of the insulating layer is etched by desmear processing so that the roughness of the upper surface of the insulating layer becomes large (e.g. about 800 nm to about 1000 nm in terms of surface roughness Ra value). When the upper surface (front surface) is roughened in this manner, it is difficult to form fine wirings on the upper surface with high accuracy. Specifically, it is difficult to form fine wirings of L/S (Line/Space)=15 μm/15 μm or less on the reinforcing material-containing insulating layer with high accuracy after the desmear processing.